I remember from my rock climbing days that there is a theory that instructions that control complex movement (what people call muscle memory) are stored in the brain as engrams. Climbers have noticed that when they take time off from training and climbing they may make rapid improvement when they resume climbing, despite losing some conditioning. The thinking went that taking time off allowed the sloppiness inherent in the practiced movement to leave the memory, leaving only the overpracticed movement. It seems like this would also apply to shooting where engrams would store the movements needed for presentations, reloads, target transitions, indexing, etc.
Brad